This invention relates to a process for determining a desired load value for a load-dependent current generating system, particularly a fuel cell system, in an electric vehicle.
German patent document DE 43 22 765 C1 discloses a process for dynamic control of the power of an electric driving unit in a vehicle which is supplied with electric energy by a fuel cell arranged in the vehicle. Based on a power demand determined from an accelerator pedal position, the mass air flow which is necessary for the fuel cell to provide the desired power is determined as a function of the instantaneous rotational speed of the electric driving motor, by means of characteristic diagrams. The air flow is then adjusted by controlling the rotational speed of a compressor arranged in the air intake pipe.
A disadvantage of this system is that an experimentally determined adjustment of the characteristic diagrams is required in order to coordinate the vehicle drive and fuel cell system. It is also a disadvantage that the air supply of the fuel cell is adapted in a time-delayed manner to an existing actual power or current value of the vehicle drive, resulting in an undersupply of air to the fuel cell during acceleration operations, and thus a rise of the probability of power breaks.
It is therefore an object of the present invention to provide a process for determining a desired load value for a load-dependent current generating system in an electric vehicle, with improved dynamics.
This object is achieved by the process according to the invention, in which a desired current value is generated directly in the driving motor converter. This arrangement has the advantage, on the one hand, that the need for adjustment of the characteristic current or power diagrams is eliminated. On the other hand, vehicle handling is improved by the provision of a front-connected air supply, so that there need no longer be an accelerator pedal limitation during acceleration, and the number of cell voltage alarms is reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.